This invention relates to the continuous casting of molten metals and more particularly to a method of introducing the molten metal into an open-ended continuous casting mold using a submerged pouring nozzle. The use of refractory pouring tubes or nozzles to introduce molten metal into a continuous casting mold is well known having been developed for the continuous casting of non-ferrous metals in the 1940's and then with the development of improved refractories, applied to the continuous casting of ferrous metals, especially steel, in the 1960's.
The primary purpose of the pouring nozzle is to protect the molten metal from oxidation as it was being cast. In the early nozzles, the molten metal was usually introduced essentially downward into the mold by a single discharge port or by a bifurcated pouring nozzle positioned beneath the surface of the molten metal contained in the mold. As example of such a nozzle is described in U.S. Pat. No. 3,371,704. Such nozzles, while reducing oxidation of the molten metal, did not completely solve the major problem of preventing oxide particles and other objectionable inclusion materials that might be present into the molten metal from being deposited near or in the surfaces of the solidifying casting and thereby becoming surface imperfections or defects in the finished casting. A major step in the solution of this problem evolved with the development of the process described in U.S. Pat. No. 3,517,726 in which the molten metal is introduced beneath the surface of the metal in the mold through controlled streams having an upwardly and outwardly flowing component which contacts the solidifying casting surfaces to wash away objectionable inclusion materials to the center of the surface of the pool of metal where they can be readily removed. This practice when applied to the continuous casting of large rectangular steel slabs significantly improved the quality of such slabs when compared to slabs cast using the earlier single port and bifurcated port nozzles.
While the practice described in U.S. Pat. No. 3,517,726 solved the problem of surface inclusions for large rectangular steel slabs, the practice did not result in consistently good results when applied to the casting of steel blooms and billets where the mold section is of smaller dimension than a slab mold section and is usually square or rectangular but having side walls not significantly greater in dimension than the end walls of the mold.